1. Field of the Invention
This invention relates to a printing device capable of ejecting a liquid mixture composed, for example, of ink and a diluent toward a recording medium, and more particularly to an improvement in arrangement of nozzles.
2. Description of the Related Art
So-called on-demand-type ink jet printer is adapted to form print images on a recording medium such as paper or film by ejecting ink droplets through nozzles in response to recording signals supplied to the printer. Recently, the ink jet printer of such a on-demand type has been rapidly prevailed due to its compactness or low manufacturing cost.
U.S. Pat. No. 5,371,529 previously filed by the present applicant, discloses the printer of such a on-demand type in which a gradation of recorded images is achieved by mixing ink and a transparent solvent as diluent at adequate proportions with each other immediately before ejection thereof. In such a printer, a concentration of the print images can be varied every recording dot, so that the printer is advantageous for obtaining a high quality duplicate of natural images such as particularly those from photographs.
The printer is of a so-called intermixing type in which ink and diluent are mixed together in an interior of the ejection nozzle.
Meanwhile, in the conventional intermixing type printing device, there has been a problem that undesired mixing of ink and diluent and, therefore, mutual diffusion proposed, in the afore-mentioned U.S. Pat. No. 5,371,529, the printer in which a one-way valve manufactured according to an electro-forming method is disposed in a boundary region between ink and diluent so as to prevent occurrence of the mutual diffusion therebetween during the stand-by period.
However, it is often difficult to completely separate ink from diluent during the stand-by period only by the arrangement of such a one-way valve. In addition, The one-way valve has another problem that its manufacturing cost is high.